1. Field of the Invention
The present invention relates generally to a flexible self-expandable stent using shape memory alloy for expanding stenosal portions and method and apparatus for fabricating the same, and more particularly to a flexible self-expandable stent using shape memory alloy and method and apparatus for fabricating the same, used to be situated in and expand the passages of stenosal portions so as to deal with the stenosis of a blood vessel caused by thrombus and the stenosis of the gullet, the gall duct and the urethra caused by cancer tissues and the formation of the artificial passage in the jugular vein, which is capable of being positioned to fit the shape of the passage of the stenosal portion regardless of the shape of the passage, such as a straight (horizontal or vertical) passage and a winding passage, while maintaining its transversal elasticity, thereby maintaining the shape of the passage and minimizing the deformation of the stenosal portion.
2. Description of the Prior Art
In general, a blood vessel is blocked or constricted because of thrombus, arteriosclerosis or the like, so a variety of disorders occur.
When a blood vessel is being constricted or has been constricted, the stenosal portion of the blood vessel is treated through artificial vessel replacement or angioplasty by means of a surgical operation.
However, such a surgical operation requires the incision of the large body region around a pathological portion, so a large scar remains, a long period of convalescence is required and the insufficient effect of an operation is achieved.
In particular, most vascular diseases are caused by hypertension and a heart disease, so it is impossible to treat most vascular disease by means of the surgical operation.
In order to overcome such a problem, there is employed angioplasty without an surgical operation, in which a small hole is bored into a femoral artery, a balloon catheter tube is inserted into a stenosal portion through the small hole from the outside of the body into the inside of a blood vessel, and the balloon of the balloon catheter tube is inflated.
However, in accordance with angioplasty, a blood vessel is re-constricted three or four months after an operation. Accordingly, angioplasty should be carried out again, so there occurs a problem that a patient should undergo pain and economic difficulty.
Excepting such vascular diseases, when the gullet is blocked by cancer tissues, it is impossible to take food through the mouth. Accordingly, a hole is formed from the abdomen to the stomach and foot is supplied to the stomach through a tube, so pain is caused to a patient and his caregivers.
The stenosis of the gall duct and the urethra, the formation of the artificial passage in the jugular vein and the stenosis and blockade of the internal organs are dealt with in such a way.
In such cases, there occurs a problem that mental or economic burden is imposed on a patient and his caregivers.
In order to solve the problems of the prior art, the present inventors filed an expandable stent using shape memory alloy and method for fabricating the expandable stent (Korean Pat. Appln. No. 98-13572). This application, as can be seen in FIGS. 1 to 4, discloses a prior art expandable stent in which a super-elastic shape memory alloy wire 1 is intersected with itself and woven to form a plurality of rhombic spaces 2 and a hollow cylindrical body 3 having a certain length, a plurality of entrance and exit bends are formed at both ends of the hollow cylindrical body 3, and both ends 6 and 7 of the super-elastic shape memory alloy wire 1 are welded together. In the placement of the expandable stent, the hollow cylindrical body 3 is considerably reduced in volume by compressing the rhombic spaces 2 and the prior art expandable stent 8 is pushed into a pathological portion B-1 within a vessel B using a guide catheter G.T and a pusher catheter P.C, thereby expanding the vessel B by pushing the pathological portion B-1 radially outwardly. Accordingly, the prior art expandable stent 8 can be semi-permanently utilized to expand the stenosal portion of the body.
The use of the prior art technology of the present inventors is described with reference to FIG. 3. The position, length and inner diameter of the pathological portion B-1 situated within the vessel B are examined by means of a fluoroscope used in angioplasty, and the required portion is firstly anesthetized.
In this state, the guide tube G.T is inserted into the vessel B to reach the pathological portion B-1, and the prior art expandable stent 8 is inserted into the guide tube G.T while being constricted in width (diameter). In this state, the prior art expandable stent 8 is pushed into the pathological portion B-1 using a pusher catheter P.C.
The expandable stent 8 positioned in the pathological portion B-1 is restored to its original shape while being removed from the guide tube G.T, and simultaneously pushes the pathological portion situated in the vessel B to expand the vessel B, thereby expanding the passage of the vessel B of the stenosal portion.
In this case, the prior art expandable stent 8, as shown in FIG. 1, has the diameter Ø 10 to 30% larger than that of an applied portion, that is, a portion of a blood vessel B, and the length L longer than that of an applied portion, that is, a portion of a blood vessel B.
In accordance with the previously filed prior art of the present inventors, the expandable stent using super-elastic shape memory alloy wire 1 and having a diameter Ø and a length L has radial and longitudinal elasticity tending to be restored to its original state unless the shape memory alloy wire 1 is forcibly compressed by external force.
However, the expandable stent 8 in accordance with the prior art can be applied to the straight line-shaped vessel B without hindrance, but is not applicable to a winding stenosal vessel B shown in FIG. 4, thereby decreasing the usability of the expandable stent 8.
The reason for this is that when the prior art expandable stent 8 is inserted into the winding stenosal vessel B, the prior art expandable stent 8 does not maintain the shape corresponding to that of the winding vessel B but is restored to its straight line (horizontal or vertical) shape. Accordingly, the vessel B is lengthened and the winding portion of the vessel B is straightened (horizontally or vertically, so the entrance of the vessel B is deformed to be narrower than its original size (t→t−a), thereby hindering the circulation of material and deteriorating the function of the expandable stent.